174 FERNS IN THEIR HOMES AND OURS. 



the plant-house at Amherst." According to Smith, 

 in England "few plant-houses are exempt from 

 the ravages of the cockroach ; " but they are not 

 often found in greenhouses on this side of the 

 Atlantic. If, however, they should be discovered, 

 traps may be set for them in the same manner as 

 for the snails. "Another insect, the Aleurodes 

 vaporarium, feeds on the cuticle of the fronds, dart- 

 ing off; when disturbed, like a flock of pigeons." 

 This insect has been observed in Salem. It be- 

 longs to the mealy-bug family, and is shown at PI. 

 22, Fig. 4, in the young or larval condition ; Fig. 

 I, full grown. 



Under certain conditions various leaf -fungi attack 

 the ferns. Among them is the "sooty mildew," 

 which quickly covers the fronds of large species. 

 The Uredo filicum Desm. assails different species 

 in the open air, as well as in the greenhouse ; and 

 frequently the fronds of Pteris aquilina will be dis- 

 figured by patches of Dothidea pteridis, Fr. t which 

 so much resembles the fructification of ferns, that 

 it is sometimes mistaken for this by inexperienced 

 persons. The same thing occurs with Aspidium 

 marginale. Only the first of these fungi does 

 much injury to the ferns. The treatment advised 

 to destroy this is " dusting with sulphur, or wash- 

 ing and syringing." Sulphur must be always used 

 with care in a greenhouse ; for should even a very 

 small quantity fall on the flues, and ignite, the 



